Radix rufescens, (J. E. GRAY, 1822) (J. E. GRAY, 1822)

Falniowski, Andrzej, Jaszczyńska, Aleksandra & Hofman, Sebastian, 2023, Radix Rufescens (J. E. Gray, 1822) (Gastropoda: Lymnaeidae), A New Species For Oman And Arabian Peninsula, Acta Zoologica Academiae Scientiarum Hungaricae 69 (3), pp. 303-312 : 305-309

RESULTS

The shell ( Fig. 2 ) with acute spire, high as for this genus, the aperture broad and variable in outline; the shell resembles the ones presented for R. rufescens in VINARSKI et al. (2020). The albuminoid gland ( Fig. 3A ) flat and rather broad, the corpus pyriformis short and bulky, bursa copulatrix small and without a discernible duct, prostate narrow, slightly broadened in its distal part, the vas deferens outlet close to the margin of the terminal part of the prostate. The praeputium ( Fig. 3B ) proximally cylindrical, distally gradually narrowing, with spots of black pigment, the penis sheath pigmentless, with moderately broadened proximal end. The length proportion between the praeputium and penis sheath was 1.25, compared with 1.09–1.27 recorded for. R. rufescens by VINARSKI et al. (2020).

The maximum likelihood tree for COI ( Fig. 4 ) clusters our Omanian specimen (bootstrap support 94%, Bayesian probability 0.99) within R. rufescens , all the other specimens of this species are from Nepal, Bangladesh, and Myanmar. The p-distance within this group was 0.017. The Omanian specimen differed from the other R. rufescens by p-distance 0.007 –0.036. The sister species of R. rufescens is R. natalensis . p-distance between these two species equals 0.092.

DISCUSSION

Our data clearly identified our Omanian specimens as belonging to Radix rufescens . Genetic differences between this specimen and the other sequences R. rufescens were much smaller than between R. rufescens and its sister species, R. natalensis . Also length proportion between the praeputium and penis sheath confirmed this species assignment. This is the first record of Radix rufescens not only in Oman, but in all Arabian Peninsula. Only five species of the Lymnaeidae , two of them representing the genus Radix , have been recorded ( SMITH 1894, BROWN & GALLAGHER 1985, NEUBERT 1998): R. natalensis , molecularly identified so far only in Africa ( SAITO et al. 2021), and R. auricularia , with a wide Eurasian range. Surprisingly, R. euphratica ( Mousson, 1874) , inhabiting Iran separated from Oman only by relatively narrow Ormuz Straight, has not been recorded from the Arabian Peninsula. Thus R. rufescens would be the sixth lymnaeid species in the Arabia. However, the shells of R. rufescens are practically indistinguishable from the ones of R. natalensis (e.g., VINARSKI et al. 2020). Thus, either R. rufescens inhabits Wadi Tiwi (and some other still unstudied localities), or simply this is the first properly identified specimen of this species, and the records of R. natalensis (at least some of them) refer to R. rufescens . On the other hand, the supposed occurrence of R. natalensis in Oman may be the result of migration from the Horn of Africa Hotspot and the Eastern Afromontane Hotspot ( MITTERMEIER et al. 2004).

The evolutionary history of Radix and main colonization routes are well known ( SAITO et al. 2021). The first diversification area was situated in east India, the rufescens / natalensis group split then into two lines. The ancestor of R. natalensis probably moved into western India, and later to Africa, R. rufescens remained in Nepal and Bangladesh both NE of the Indian Subcontinent, as well as in Myanmar at Malay peninsula. How R. rufescens colonized Wadi Tiwi remains enigmatic. One of the excellent maps of SAITO et al. (2021) we have completed with our finding ( Fig. 5 ). The known area of occurrence of R. rufescens may be much wider than the molecularly identified individuals confirm, thus the population discovered by us may be a part of the range covering perhaps the entire Indian Peninsula, southern Pakistan and Iran, and a large part of the Arabian Peninsula. Obviously, migration from the western coast of India would be more probable. Some older migrations may have been possible at the time when the Persian Gulf was reduced to a series of freshwater lakes (LAMBECK 1996).

However, small genetic differences between R. rufescens from Oman and from Nepal, Bangladesh, and Myanmar suggest much younger episodes of migration. Arabian Peninsula, especially Oman, since about 2,200 BC ( PAINE 2013) was in trade relations with India. Arabian dhow sailed with monsoon winds ( MILES 1919, LEBARON BOWEN 1949, VILLIERS 2018), conveying food, timber, etc., thus the accidental transportation of eggs or adult specimens of aquatic snails was probable. Especially the barrels and cans with drinkable water for the crew, rinsed before refilling in the stream in the outlet of Wadi Tiwi (situated not far from Sur, for centuries the main port at this region) were suitable for such transportation. The anthropogenic transportation of snails is extremely common ( PRESTON et al. 2022). Also transportation by birds cannot be excluded ( CHARALAMBIDOU & SANTAMARIA 2002, FIGUEROLA & GREEN 2002).

Figures

Fig. 2. Shells and mantle pigmentation of Radix rufescens. Scale bar: 5 mm

Fig. 3. Reproductive organs of Radix rufescens: A = ventrally, B–C = praeputium and phallotheca (ag – albuminoid gland, cp – corpus pyriformis, hg – haermaphrodite gland, ng – nidamental gland, ph – phallotheca (penis sheath), pr – prostate, prae – praeputium, ut – uterus, v – vagina, vd – vas deferens). Scale bar: 1 mm

Fig. 4. Maximum likelihood tree computed for COI; bootstrap supports/Bayesian probabilities and GB numbers are given

Fig. 5. Hypothetical way of invasion of R. rufescens, after SAITO et al. (2021), modified